An NMR investigation of lithium occupancy of different sites in the oxide superconductor LiTi2O4 and related compounds

The changes in lithium site occupancy as LiTi2O4 changes phase through the spinel to ramsdellite solid state phase transition are monitored by a Li-6 NMR investigation of quenched samples, using magic angle spinning. Other lithium/titanium/oxygen compounds are studied as references for lithium environments. The 8a/16d 3:1 partition of lithium in Li4Ti5O12 is confirmed quantitatively. Lithium is found in several environments as a function of quenching temperature, and we discuss the assignment of the NMR responses to these different environments. These NMR studies, along with diffraction measurements, confirm that the spinel to ramsdellite transition is indirect, with two phases of changing composition coexisting between the spinel and the ramsdellite LiTi2O4 forms. (C) 2000 Academic Press.